Theoretical Study of Elementary Steps in the Reactions between Aluminum and Teflon Fragments under Combustive Environments

Gas-phase reactions between aluminum particles and Teflon fragments were studied to develop a fundamental understanding of the decomposition reactions and combustion processes of the Al-Teflon composites. The reactions were investigated theoretically using ab initio calculations at the MP2/aug-cc-pVDZ level, with the final thermokinetic data obtained with coupled cluster theory (CCSD(T)/aug-cc-pVTZ). Among reactions under oxygen-lean conditions, CF3 + Al -> CF2 + AlF channel is the fastest, followed by the CF2 + Al -> CF + AlF and CF + Al -> C + AlF channels. Under oxygen-rich conditions, reactions of COF with aluminum are probed to be faster than those involving COF2 species. Reaction path multiplicity has been considered. Our results show that multiplicity plays a very important role in determining the reaction order, that is first order or addition-elimination reactions of Al with CF3 are predicted to be faster than those proceeding through direct abstraction or second order. In addition, the present kinetic model suggests that CF3 + Al -> CF2 + AlF with m = 1 and COF + Al -> CO + AlF channels are very competitive under the same thermal conditions. The computed enthalpies of reaction are systematically compared with the available literature. The predicted kinetic model and its time constants (tau) are in good qualitative agreement with experimental observations of the reactions between Al nanoparticles and Teflon for the 500-1200 K temperature range.